Previous laser seeders for remote-sensing lidars generate required wavelength-stepped pulse trains by combining multiple externally amplitude-modulated lasers. Using multiple fixed-wavelength lasers and corresponding multiple modulators may cause issues with respect to the reliability and measurement performance, as well as increase power consumption, size, mass, and cost. Thus, it may be desirable to replace the fixed-wavelength distributed feedback laser diodes and their modulators with a single precision fast wavelength-scanning laser and a modulator to drastically simplify the seeder architecture and to eliminate the optical crosstalk among different wavelength channels.
The wavelength of widely-tunable monolithic semiconductor diode lasers has been fast switched and locked within ˜12 μs for a step size over 30 nm. Limited by the coarse frequency locking techniques employed in such demonstrations, the uncertainty of the locked laser frequency was as large as a few GHz, too large for many demanding applications. One or more embodiments of the present invention may drastically improve the frequency precision while retaining the fast tuning speed of such widely tunable lasers. The embodiments of the present invention may add fast tunability to an existing phase locked loop technique that offset-locks a slave laser to a frequency stabilized reference laser line.